Devil May Cry walkthrough/M18

Walkthrough part 1
Watch the awesome cutscene of Dante mastering the Sparda! When control is given back to you, step on the portal in the floor. You'll be taken back to the watchman's room, and now the other mirror on the wall will be activated. Jump through it to enter the Mirror World.

Dante will immediately be thrown into an underwater prison. Shoot the barrels in the cell you're in to liberate some Red Orbs, then follow the floating red orb through the hole in the wall. There are two more cells in this next area, and you will want to explore them fully before continuing.

The cell directly across from you has a mess of red orbs on the bed. Swim near to collect them all. When you turn around and swim out, shoot the barrels to your right, and continue swimming down the hall to your right. When you hit the wall, turn into the cell on your left and shoot the lone barrel there for a Blue Orb Fragment. Swim out of the cell and continue down the hall that's across from you.

The room you zone into will have three Sin Scissors in them. They aren't hard: just let them float away from the walls and blast them a few times with your needlegun. If you shoot them when they're too close to the wall, they will stagger through the wall and be invulnerable until they recover. Defeating them will open the door to the next area.

Swim through the door between the horse reliefs and Dante will end up back on dry land. Freaky. Walk forward, collect the red orbs hanging around, and go through the door with the lion face. You will be in a shaft resembling the one you entered the waterways way back in Mission 4, with stairs spiraling up around the outside. To get another Blue Orb Fragment, climb up the stairs until your way is bocked by rubble. There will be a platform protruding from the wall near there. Jump onto it to nab the fragment.

Activate the shield device on the wall to fill the room with water. Swim quickly to the top of the shaft. When the water recedes, grab the Philosopher's Egg from its pedestal. Run down the stairs, jumping over the gabs when necessary. About half way down, there is a small wood-colored door. Enter it.

You will be in a courtyard almost exactly like the one where you first encountered the Shadow, except this one is inversed. The collapsed stairs are on your right instead of your left, and there is no fountain in the center. There are, however, some familiar rainbow-colored pools on the ground, and shield devices on the walls. Uh-oh. Approach and examine the flames in the alcove and use the Philosopher's Egg. It may take some time to transform, so Dante's going to have to sit around on his hands and wait.

Psych!

Boss: Nightmare
The pile of nether-sludge returns! See Mission 16 for strategy on beating it. This encounter is exactly the same except for the terrain, and Nightmare learns one new trick:
 * Round Trip - When at low health, Nightmare will spawn a spinning helicopter blade that will fly around and attempt to slash through Dante. Jump to avoid it.

Walkthrough part 2
Grabbing the Elixir from the fire will end the mission, but there is more to be done here! Wall Hike or Air Hike up to the broken walkway on the left side of the courtyard and enter the door here. Grab the red orbs in the hall way, and at the farthest end is a Blue Orb Fragment. You can also grab this fragment in the next mission.

Go back to the courtyard and pick up Elixir to end the mission and spawn a red portal.